Acoustic device



I May 14-, 1935 A. L. THURAS ACOUSTIC DEVICE Filed May 10, 1933 B 6 3 M 2 u a. a 27 .8 la lz IN 5 N TOR v A. 1.. THUR/4S BY AT TORNEV Patented May 14, 1935 PA m ACGUGTIC Albert. 12. Thuras New York, N. Y.,, assignor to Belt Telephone Laboratories; Ihcorporatedi; New Yorltylfl. Y2, at corporation of New Fork Application Mau 1t, 1933, serial. No. 510.291

solemn. rein. net-11515) This invention relates to an. acoustic device: and more: partieularlyyto electrodynamm or moving ccilntnansmitten An: object of; .thQEaEiMVBH-fiOm'iSLtD construct or smalls, compact,.-and; efficient manning: coil mittenofiun-ttorm: responsethat may-he: readily carriedcmtheperson. L V

A further object-of the invention. is to ac curately center the coil of an electrodynamzin: deyieerin the: air -gap'of the: device-..

A: flea-tare of. this. invention comprises am e 21-" trodynamie deyiceqinr, which; a. tubular: casing open at eaelr Lend. houses; the; magnet strnctince,v

diaphragm and-@coil; ct, the den-ice and a. 'ter-: 1 x minal carrying; member; a the: terminal carrying member andvthemagnetbeing separated by a spacermember or: redi, eaclrfunctioningi to close one.- open and ot the: casing; and. being; slidably remevablez therefromv i i magnet--strueturehaving; a. eentrat and. an outer pols tlireslatter supporting am outer pole: piece: that carries a; diaphragm. to which; a.- ceil. is attached. The; outer pol-e piece: has; a flange or depending. portion having: membersprotectsing therefrom to engage with slots in the magnet outeir pole whereby, the coil is centered in the air-gap defined by the outer and the center pole pieces. A more complete understanding of this invention will be obtained from the detailed description which follows read with reference to the appended drawing, wherein:

Fig. l is an elevational sectional view of the acoustic device embodying this invention;

Fig; 2 is a plan view, partly broken away, of the device of Fig. l;

Fig. 3 is a sectional view of the device of Fig. 1 along the line 3-3 thereof; and

Fig. 4 is an exploded view of the device of Fig. 1 partly broken away and partly in section.

There is shown by the drawing an acoustic device, designated generally as Ill, comprising a microphone or transmitter unit, designated generally as I l, of the electrodynamic or moving coil type. The transmitter unit comprises a magnet having a center pole l2 including a dome-shaped pole piece or cap member l3 secured to its upper end by suitable means, such as the screw M, and an outer, cylindrical pole I5 whose inner surface l6 tapers outwardly. An annular outer pole piece H is supported by the outer pole and defines with the member l3 an annular air-gap I8. The member I'Icarries or supports a diaphragm Hi. This diaphragm, which is pref- A furtherfeatare of the intention. comprises- 61131315,! of. a light. weight high-strength material, such dnralumin, cnmprises a: central. stiffened; dome-shaped portion 26-; an outer peripheral portion 2|, which is securedagainst the outer pole piece.- bna. clamping, ring 23 and suitable fastening means',, such as screws: 23:; and an. intermediate flexible portion M.. A. coii' 25; pref-- erablm or the. edgewound type, is attached to the at the junction of. the portions. 211' and; Hand is supported, in and adapted for movement ,in'. the; air-gap, t8

The: outer, pole .pieceais provided: with a alepending: flange portion 2 6; extending into themagnet cavity its enter surtace being tapered reversely with respect to the inner surface It of the: enter pole so: as: to;- make a. snug: and; sliding fit. therewith. Extending: radially -ir0m the: flange 2S and, substantially at, right angles: to: it, are pin: members 2-8-= which are spaced apart at less. than. 180-; These pins engage. with or rest in: similarly spaced; radially extending slots 23 in the magnet outer pole; This. flange and. pin arrangement insures properinitial centering of. the coil in the air-gap and; proper and accurate: recentering; thereof. if for reason the outer pole. piece. should be. temporarily detached from" themagnet. u

A ring or plate member 30 having radially extending arms 3| is secured to the under surface of the outer pole piece, being fastened thereto by screw members 32. The member 35) has a machined portion 33 provided with a ridge 34 spaced from and forming with the under surface of the outer pole piece, a restricted, annular slot 35 through which, when the diaphragm isvibrating in response to sound wave impulses, air may flow between the magnet chamber or cavity 21 and the chamber 36 between the diaphragm and magnet structure. A sealing member 31 frictionally held on the center pole prevents air movement other than through the slot 35. The base of the magnet is provided with a plurality of drillings, apertures, or passages 38 through one of which extends an elongated tubular member 39 which is supported from the plate pole, having an opening to the atmosphere adjacent the peripheral portion of the diaphragm.

The transmitter unit H is positioned in one opened end of a tubular, cylindrical case or housing 4|. It is slidably insertable through the lower end of the case and is prevented from sliding out at the upper end by an internal flange 43 against which rests the peripheral portion of the outer pole piece. The upper end of the case 4| is covered by a dome-shaped protective screen 44, preferably of wire gauze, of such a mesh, however, that will not impede the passage of sound waves to the diaphragm.

A terminal carrying member or disc 45, preferably of insulating material, is positioned in the lower end of the case, and, at its periphery, bears against the seating surface 46. It is maintained in position by a lock ring or member 41 externally threaded at 48 for engagement with the internally threaded end portion 49 of the case. The terminal member and the transmitter unit are spaced apart by a spacer member in the form of a rod 50, preferably of. nonmagnetic material, which may be secured to the terminal member, for instance, by the screw 5|, and which bears against the central phere through the tubular member 39. A damping element 56, in the form of a cloth annulus, is fastened to the magnet over the passages and prevents undesirable resonance of the chambers connected through the passages.

This acoustic device, which is shown much enlarged in the drawing, is adapted to be con venientlycarried in the jacket pocket of a user or on the lapel of his coat, being supported, for

instance, by a clip (not shown) attached to the case and adapted to engage with the users clothing. The device is small, compact, readily assembled and disassembled, efficient, and of substantially uniform response over the frequency range to be translated.-

Although this invention has been disclosed with reference to a specific embodiment, it is to be understood, of course, that it is capable of modification without departing from the spirit of the invention, the scope of which is to be considered as limited only by the appended claims.

What is claimed is:

1. An acoustic device comprising a magnet having a central pole piece, an outer pole having a rim portion containing two radial slots located on different diameters, an outer pole piece carried by the outer pole and forming an air-gap with the central pole piece, a diaphragm supported by said outer pole piece, and a coil attached' to said diaphragm and adapted to be positioned in said air-gap, said outer pole piece having twomembers extending radially therefrom for engagement with said slots to center said coil in said air-gap.

2. An acoustic device comprising a magnet having a central pole, an outer pole having a rim portion containing two radial slots spaced apart at less than an outer pole piece carried by said outer pole and forming an air-gap with the central pole, a diaphragm supported by said outer pole piece, a coil attached to said diaphragm, said outer pole piece having a depending flange, and radially extending members on said flange for engagement with the slots whereby said coil is centered in the airgap.-

3. An acoustic device comprising a magnet having a central pole piece, an outer pole having a rim portion'containing two radial slots located on difierent diameters, the inner surface of said pole piece'tapering outwardly, an outer pole piece carried by said outer pole and forming an air-gap with the central pole, a diaphragm supported by said outer pole piece, a coil attached to saiddiaphragm and adapted to be positioned in said air-gap, said outer pole piece having a depending flange portion whose outer surface tapers revers'ely with respect to theinnersurface of said outer pole and which fits within the rim portion of the outer pole, and members extending radially from said flange-portion and resting in said radial slots.

' ALBERT L. 'IHURAS. 

